Add Export Day Segments option for multi-day routes

When a route has overnight waypoints, the export dropdown shows a
third option: "Export Day Segments" which downloads one GPX file per
day. Each file is named day-N-start-name.gpx with the day's track
segment. Only visible when the route has multiple days.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/i18n/src/locales/de.ts

@@ -22,6 +22,8 @@ export default {
     exportRouteDesc: "GPX-Track für jede App",
     exportPlan: "Plan exportieren",
     exportPlanDesc: "Mit Wegpunkten und Sperrzonen",
+    exportDays: "Tagesetappen exportieren",
+    exportDaysDesc: "Eine GPX-Datei pro Tag",
     "undo.tooltip": "Rückgängig (Strg+Z)",
     "redo.tooltip": "Wiederholen (Strg+Umschalt+Z)",
     importGpx: "GPX importieren",

packages/i18n/src/locales/en.ts

@@ -22,6 +22,8 @@ export default {
     exportRouteDesc: "Clean GPX track for any app",
     exportPlan: "Export Plan",
     exportPlanDesc: "Includes waypoints and no-go areas",
+    exportDays: "Export Day Segments",
+    exportDaysDesc: "One GPX file per day",
     "undo.tooltip": "Undo (Ctrl+Z)",
     "redo.tooltip": "Redo (Ctrl+Shift+Z)",
     importGpx: "Import GPX",